Investigation of Molecular Assisted Recombination Detachment Physics in Fusion Relevant Hydrogen Plasmas

The Molecular Assisted Recombination (MAR) regime is investigated in hydrogen plasmas in both a linear divertor simulator device, the York Linear Plasma Device, and a Gaseous Electronics Conference standardised reference cell. The aim of this work has been to characterise both the negative ion population within the YLPD and the significance of the surface material choice in divertors by using a well known plasma source in the form of the GEC. Hollow radial pro�les with varying pro�le shapes and absolute maxima have been found for negative ion densities on the YLPD with good spatial resolution. The fraction of H- has been found to typically lay within 10% of the electron density for most pressures which is in agreement with previous work. Rotational gas temperatures have been found to be around 400-700 K on the YLPD in an MAR state while vibrational temperatures were estimated at 2000-3500 K, also in agreement with literature. The results on the GEC cell for surface effect on negative ion production for stainless steel, tungsten and molybdenum have shown significant differences, the causes of which are not yet fully understood. There was enhancement of negative ion production for both steel and tungsten when compared to molybdenum at 25 Pascals pressure. The trends of negative ion density with applied radio frequency power 9 mm above the samples were similar between materials however the curves appear to be shifted along the power axis based on the specific material as well as scaled in their respective maxima. It is hoped that these measurements will assist in the improvement of MAR understanding and modelling for future research with applications in tokamak divertor design, linear device study and simulation as well as potential broader applications in negative ion devices. The overarching aim is to improve the understanding of MAR negative ion production for divertor optimization.